The preparation of composite structures suitable for subsequent deposition of a thick film is critical to a number of technical areas. For example, composite structures with a thick film include ferroelectric structures, photovoltaic structures, and superconducting structures. If the ultimate structure is used as a ferroelectric or photovoltaic structure, then the thick film may be a conductive oxide, ferroelectric material, a ferromagnetic material, a piezoelectric material, an insulating material, or a semiconductive material. If the ultimate structure is used as a superconducting structure, then the thick film may be a high temperature superconductor (“HTS”) (e.g., yttrium barium copper oxide (“YBCO”)).
A composite structure coated with a HTS thick film is commonly referred to as a coated conductor. The standard architecture for the coated conductor's composite structure using an ion beam assisted deposition (“IBAD”) template is either: (1) base substrate/aluminum oxide (“Al2O3”)/yttrium oxide (“Y2O3”)/IBAD-magnesium oxide (“MgO”)/homoepitaxial-MgO/lanthanum manganate (“LaMnO3”) or strontium ruthenate (“SrRuO3”) or strontium titanate (“SrTiO3”) or mixtures of SrRuO3 and SrTiO3, or (2) base substrate/erbium oxide (“Er2O3”)/IBAD-MgO/homoepitaxial-MgO/LaMnO3 or SrRuO3 or SrTiO3 or mixtures of SrRuO3 and SrTiO3. The composite structure is then coated with a HTS thick film such as YBCO.
The LaMnO3, SrRuO3, SrTiO3, and mixtures of SrRuO3 and SrTiO3 layer in the composite structure's standard architecture serves as a buffer material. Although these buffer materials result in coated conductors with high critical current densities (“Jc”), they are problematic for cost-effective, long-length coated conductor production. For example, each of these buffer materials require a homoepitaxial MgO layer on top of the IBAD MgO. The slow deposition rate of the homoepitaxial MgO layer affects the coated conductor's cost of production. Moreover, the difficult control of stoichiometry and the slow deposition rate make these buffer materials unpopular in industry.